Method of forming protective coating on cell safety valve element, cell safety valve element, cell safety valve element coated with protective film, cell sealing plate using the element, and enclosed cell using the plate

ABSTRACT

A method of forming a protection film of a safety valve element for battery prevents corrosion. The safety valve element is composed of a safety valve element having a metal substrate with a perforated pore and a metal foil laminated on a metal substrate so as to cover the pore, and a protection film is formed by coating an organic coating at least on one side of the safety valve element.

RELATED APPLICATIONS

The present application is continuation of co-pending parent applicationSer. No. 09/601,474, nationalized Oct. 17, 2000, which application wasthe U.S. national stage of international application PCT/JP99/00393,filed Jan. 29, 1999.

FIELD OF INVENTION

The present invention relates to a method of forming a protection filmof a safety valve element, a safety valve element covered with aprotection film, and a battery using same which prevents from corrosionof a metal part of a safety valve element used for bursting-proof of aclosed battery.

BACKGROUND OF THE INVENTION

A closed battery using an alkali metal like lithium as a material forpositive and negative electrode has been widely used in recent years.These batteries need sealed structure so that an alkali metal likelithium may not react with moisture in an atmosphere, but a completelyclosed structure sometimes causes a bursting of battery provokedabnormally elevated pressure in the battery when the battery is exposedto high temperature or it is inappropriately handled at the charge ordischarge.

It is disclosed that a closing plate for a battery provided with abursting-proof mechanism or a safety valve for releasing a pressure in abattery when it is abnormally elevated.

For example, Japanese Patent Laid-open Publication No. HEI-5-84025discloses a safety valve device for a closed battery which provide a gasreleasing opening in a positive electrode terminal constituting aclosing plate for a battery and a metal foil welded for bursting-proof.

In this closing plate for a battery, when a pressure in a battery iselevated, a metal foil for bursting-proof ruptures so that a pressurereleases through a gas releasing opening applied in a positive electrodeterminal.

When electrolyte is filled up in a battery container, electrolytesometimes scatters and adheres the outside of it. Especially, in case oflithium ion battery, a non-aqueous electrolyte including lithiumfluoride as a supporting electrolyte is used for electrolyte.

This fluoride does not attack a metal part of a battery container and asafety valve, but it has strong corrosion so as to absorb moisture inatmosphere and to change into hydrofluoric acid.

For this reason, it is a problem that the electrolyte scatters andadheres to the outside of a battery container, especially the metal foilof a safety valve element, and that a thin metal foil is perforated bycorrosion.

The present invention provides a method of forming a protection film ofa safety valve element for a closed battery, a safety valve elementcovered by a protection film, a closing plate using same and a closedbattery using same which prevents corrosion of a metal part by coveringthe safety valve element for battery by a protection film.

DISCLOSURE OF THE INVENTION

The present invention is a method of forming a protection film of asafety valve element for a battery comprising a metal substrate havingperforated pores and a metal foil laminated on said metal substrate soas to cover said perforated pores, wherein an organic coating is coatedon at least one side of it.

Further, it is a method of forming a protection film of a safety valveelement of a battery comprising a metal substrate having perforatedpores and a metal foil laminated on said metal substrate so as to coversaid perforated pores, wherein an organic resin film is laminated on atleast one side of it.

Furthermore, it is a method of forming a protection film of a safetyvalve element of a battery comprising a metal substrate havingperforated pores and a metal foil laminated on said metal substrate soas to cover said perforated pores, wherein an organic coating is coatedon at least one side of covering portions of said metal foil.

Further, it is a method of forming a protection film of a safety valveelement for a battery, wherein an organic coating is coated on a safetyvalve element for a battery comprising a metal substrate havingperforated pores and a metal foil laminated on said metal substrate soas to cover said perforated pores after said safety valve element for abattery is applied on a closing plate for a battery container having aperforated pore which is to be a valve opening of a safety valve so thatsaid perforated pores of said metal substrate of safety valve elementfor a battery and said perforated pore of said closing plate areconnected through, and said metal substrate and said closing plate areadhered together using adhering means so that both adhere around saidperforated pore of said closing plate, and it is characterized that saidmeans is laser beam welding.

Further, the present invention is a safety valve element for a batterycomprising a metal substrate having perforated pores and a metal foillaminated on said metal so as to cover said perforated pores, wherein aprotection film is covered on at least one side of said safety valveelement for a battery.

It is characterized that said protection film is a coated film of anorganic coating or a laminated film of an organic resin film.

Further, it is a safety valve element for a battery comprising a metalsubstrate having a perforated pore or a first hole extendingtherethrough, and a metal foil laminated on said metal substrate so asto cover said perforated pore, wherein a protection film is covered onat least one side of covering portions of said metal foil of a safetyvalve element for a battery, and it is characterized that saidprotection film is a coated film of an organic coating.

Further, the present invention is a closing plate, wherein said safetyvalve element for a battery is applied on a closing plate for a batterycontainer having a perforated pore or a second hole extendingtherethrough which is to be a valve opening of a safety valve so thatsaid perforated pore of said metal substrate of safety valve element fora battery and said perforated pore of said closing plate are connectedthrough, and said metal substrate and said closing plate are adheredtogether using adhering means so that both adhere around said perforatedpore of said closing plate, or a closing plate, wherein said safetyvalve element for a battery comprising a metal substrate havingperforated pores and a metal foil laminated on said metal substrate soas to cover said perforated pores is applied on a closing plate for abattery container having a perforated pore which is to be a valveopening of a safety valve so that said perforated pores of said metalsubstrate of safety valve element for a battery and said perforated poreof said closing plate are connected through, and said metal substrateand said closing plate are adhered together using adhering means so thatboth adhere around said perforated pore of said closing plate, and afterthat an organic coating is coated on said safety valve element for abattery, and it is characterized that said adhering means is laser beamwelding.

Furthermore, the present invention is a closed battery, wherein anelectrode comprising a positive electrode, a negative electrode and aseparator is packed with electrolyte into a battery container and anopening portion of said battery container is closed so that said aclosing plate for battery is put into and fixed around innercircumference of said opening portion of said battery container.

BRIEF DESCRIPTION OF A DRAWINGS

FIG. 1 is schematic sectional view showing an example of a safety valveelement covered by protection film of the present invention.

FIG. 2 is schematic sectional view showing the other example of a safetyvalve element covered by protection film of the present invention.

FIG. 3 is schematic sectional view showing another example of a safetyvalve element covered by protection film of the present invention.

FIG. 4 is schematic sectional view showing an example of a closing plateof a battery having a safety valve element adhered to it.

FIG. 5 is schematic sectional view showing the other example of aclosing plate of a battery having a safety valve element adhere to it.

FIG. 6 is schematic sectional view showing another example of a closingplate of a battery having a safety valve element adhere to it.

FIG. 7(a) is schematic sectional view showing an example of a closingplate of a battery having a safety valve element adhered to it before itis covered by a protection film.

FIG. 7(b) is schematic sectional view showing an example of a closingplate of a battery having a safety valve element adhered to it after itis covered by a protection film.

FIG. 8 is schematic sectional view showing another example of a closingplate of a battery having a safety valve element adhere to it.

BEST MODE FOR CARRYING OUT THE INVENTION

The examples of a safety valve coated with a protection film and amethod of making a protection film of the present invention are nowexplained below with reference to drawings.

EXAMPLE 1

FIG. 1 and FIG. 2 are sectional views which show the examples of asafety valve element coated with a protection film of the presentinvention.

As shown in FIG. 1, a safety valve element 10 is provided with aprotection film 3 formed on a metal foil 2 of a laminated board 5 whichis laminated with metal foil 2 so as to cover perforated pore 4 on oneside of a metal substrate 1 having perforated pore 4 which is to be anopening of a safety valve.

As shown in FIG. 2, a safety valve element is provided with a protectionfilm 3 formed on a metal substrate 1, a side wall portion of perforatedpore 4 and a portion where metal foil 2 covers perforated pore 4.

That is, a protection film 3 covers all around cavity which is composedof metal foil 2 and perforated pore 4 formed on a metal substrate 1 andconnects with a protection film 3 covering a metal substrate 1.

As examples are shown in FIG. 1 and FIG. 2, a protection film 3 isformed at least on the whole surface to be the outside of safety valveelement 10 in a battery container.

Each safety valve element 10 of the present invention is produced asfollows.

At first, a strip of laminate 5 is produced by laminating metal foil 2on one side of a strip of metal substrate 1 having plural numbers ofperforated pore 4 to be the opening of valve so as to cover theperforated pore 4.

Though perforated pore 4 is usually circle having a diameter of 1 to 10mm, it may be oval having major axis of 1 to 10 mm or polygon havingsame size of the circle with said diameter.

Further, a form of perforated pore 4 can be a segment having a certainwidth (for example, straight or curved slit etc.) or geometric patterncombined with said figures.

It is preferable that perforated pore 4 is geometrically arranged insuch a pattern of lattice, zigzag or a like, and pitch of eachperforated pore 4 is properly selected by the required size of a safetyvalve material.

Perforated pore 4 can be formed from a thin cold-rolled metal sheet byusual perforating method such as punching press or etching.

Metal substrate 1 forming perforated pore 4 as mentioned above and metalfoil 2 are cold-pressure-bonded in a vacuum using a method for exampledisclosed in Japanese Patent Laid-open Publication No. HEI-1-224184.

That is, after activating a surface of a metal substrate 1 and a metalfoil 2 to be laminated each other by spattering in etching chamber, theyare cold-pressure-bonded using a rolling unit in a vacuum chamber.

Thus, a strip of laminate 5 of the present invention is produced.

In an example shown in FIG. 1, a protection film 3 is formed by coatingand subsequent drying or baking an organic resin coating on wholesurface of a metal foil 2 of a strip of laminate 5 produced as mentionedabove.

Further, a protection film 3 is formed by laminating an organic resinfilm on whole surface of metal foil 2 of a strip of laminate 5.

In this way, a strip of laminate covered by protection film whereinplural numbers of perforated pore 4 formed on a metal substrate 1 arecovered by metal foil 2 and protection film 3.

A lot of safety valve elements 10 for battery can be obtained from astrip of laminate covered by a protection film by punching in such amanner that at least one perforated pore is included in each safetyvalve element.

In a example shown in FIG. 2, a protection film 3 is formed by coatingand subsequent drying or baking an organic resin coating on the wholesurface of the side which is a metal substrate 1 of a strip of laminate5, a side wall portion of perforated pore 4 formed on a metal substrate1 and a portion where metal foil 2 covers perforated pore 4.

Coating is carried out by spraying or dripping a liquid coating intoperforated pore.

In this way, a strip of laminate covered by a protection film whereinplural numbers of perforated pore 4 formed on metal substrate arecovered by metal foil 2 and metal substrate 7 and a side wall portionand bottom portion of perforated pore 4 are covered by protection film3.

A lot of safety valve elements 10 for battery can be obtained from astrip of laminate covered by protection film by punching in such amanner that at least one perforated pore is included in each safetyvalve element.

Said metal substrate is preferably any of steel sheet, stainless steelsheet, copper sheet and aluminum sheet.

The sheet thickness is usually 0.03 to 0.50 mm from the point of view ofstrength, economy and adhesion to a closing plate for battery containerand 0.05 to 0.10 mm is more preferable.

A safety valve element for battery of the present invention aims tooperate at a low pressure 30 kgf/cm² or less, preferably 20 kgf/cm² orless.

Therefore, the thickness of a metal foil of the present invention ispreferably 5 to 50 μm.

If the thickness is 5 μm or less, it easily fractures by an impact likea fall when it is applied to a safety valve for battery or like.

On the other hand, if the thickness is 50 μm or more, it is notfractured by a pressure of 30 kgf/cm² or less even when a metal having asmall tensile strength is applied, but fractured only when high pressureis loaded, a battery container itself burst, fragments scatter, andelectrolyte sputter out scatters, which causes damage of safety declinesand disadvantage of cost.

Metal foil is preferably any of steel foil, stainless steel foil, copperfoil, aluminum foil, nickel foil and nickel-iron alloy foil.

Further, it is possible to use every metal foil as long as it is stableagainst electrolyte which is filled in a battery container, and it isnot corroded and a large amount of reacted gases is not generated.

It is possible to use metal foil of zinc, lead, copper alloy such asbrass, bronze, phosphor bronze, gun metal or monel, aluminum alloy suchas duralumin and so on in addition to the above metal foils.

Above mentioned organic resin coating is preferably coating of fluorinecontained resin, epoxy resin, vinyl resin, urethane resin, polyesterresin and acrylic resin, which is coated by any of spray coating, rollcoating, bar coating and brush coating and so on.

Further, said organic resin film is preferably film which is producedfrom any of polyolefin resin, polyester resin, polyamide resin,polycarbonate resin and poly vinyl chloride resin.

Those resin films are directly adhered to be above mentioned laminate bythermally melt-bonding or sticked to be it by interposing primer.

The thickness of those organic resin coating or film is preferably 1 to30 μm, more preferably 5 to 20 μm.

If the thickness is 1 μm or less, it is difficult to completely coatmetal foil of a coating foundation in the case of coating, and it isvery difficult to make film in the case of a resin film.

On the other hand, if the thickness is 30 μm or more, it is notfractured at a prescribed loading pressure but fractured only when aloading pressure exceeding the prescribed fracturing pressure is loaded,which causes damage of safety and disadvantage of cost.

EXAMPLE 2

FIG. 3 is a sectional views showing another example of a safety valveelement for battery covered by a protection film of the presentinvention.

As shown in FIG. 3, a safety valve element 10 of the present inventioncan be provided with a protection film 3 in such a manner that anorganic resin is dripped and dried for solidifying at portion 4 a ofmetal foil 2 where metal foil 2 covers perforated port 4 formed onlaminates composed of metal substrate 1 having perforated pore 4 whichis to be the opening of safety valve covered by metal foil 2 so as toclose perforated pore 4.

EXAMPLE 3

The produced safety valve element 10 of the present invention is shownin FIG. 4˜FIG. 6.

The perforated pore 4 of a metal substrate 1 of a safety valve element10 and perforated pore 7 of a closing battery 6 for battery container isput together so as to overlap both, and then a safety valve element 10is adhered by a method of laser beam welding a round perforation 7.

FIG. 4 shows the case that a safety valve element having a structureshown in FIG. 1 is adhered to a closing plate for a battery container.

FIG. 5 and FIG. 6 show the case that a safety valve element having astructure shown in FIG. 2 and FIG. 3, respectively is adhered to aclosing plate of a battery.

The method of adhering is not only said laser beam welding but also anymethod of adhering using adhesive such as thermosetting resin adhesiveand thermoplastic resin adhesive and rubber adhesive as long asnecessary adhering strength is obtained.

Though FIG. 4˜6 show the case of adhesion that one of perforated pore 7of a closing plate 6 for a battery and one of perforated pore 4 of ametal substrate 1 of a safety valve element 10 are connected through soas to overlap both pores and then both is adhered, but it is possiblethat one of perforated pore of a closing plate 6 for a battery andplural numbers of perforated pore 4 of a metal substrate 1 of a safetyvalve element 10 are connected through so as to overlap both pores andthen both is adhered.

Said closing plate is preferably any of the same steel sheet, stainlesssteel sheet, copper sheet, aluminum sheet as above mentioned metalsubstrate.

Thickness of a sheet is usually 0.03 to 0.50 mm from point of view ofstrength, economy and easiness of adhering to a closing plate of abattery, and 0.05 to 0.10 mm is more preferable.

EXAMPLE 4

Further, as shown in FIG. 7(a) and FIG. 7(b), a closing plate for abattery container to which a safety valve element for a battery coveredby a protection film of the present invention can also be produced.

After a perforated pore 4 of a metal substrate 1 of a safety valveelement 10 and a perforation 7 of a closing plate 6 of a batterycontainer is put together so as to be overlapped, both are glued by amethod of a laser beam welding around a perforation 7 as shown in FIG.7(a).

As shown in FIG. 7(b), there can be provided a protection film 3consisting of an organic coating on a safety valve element of a batterywhich include a weld part.

Like this, because a protection film is coated on both a metal foilwhich blockades perforation and a naked metal part of a safety valveelement welded by a laser beam, a metal part cannot be attacked inwhenever corrosive electrolyte adheres.

EXAMPLE 5

Though FIG. 4˜FIG. 7 show structures of that perforated pore 4 ofoverlapping a perforated metal substrate 1 of a safety valve element 10and perforation 7 of a closing plate 6 so as to put in and glue a safetyvalve element 10 whose diameter is equal to that of perforated pore 7 ofa closing plate 6 to perforated pore 7 of a closing plate 6, it ispossible to pile and glue a safety valve element 10 whose diameter isbigger than that of perforated pore 7 to a closing plate 6.

A closing plate of a battery which adhere a safety valve element coatedwith a protection film blockade a opening of said battery containerwhich electrode support to put in with electrolyte and a closing batteryof the present invention is made.

Possibility of Use in Industry

The present invention is a method of forming a protection film of asafety valve element of a battery and a safety valve element using it.

There is provided a protection film of safety valve element coated withan organic coating or a film of an organic resin at least one side of asafety valve element which consist of a perforated metal substrate and ametal foil laminated on said perforated substrate so as to blockade saidperforation.

Further, the present invention is a closing plate for a closed batterycharacterized that the closing plate for a battery container having aperforated pore which is to be the opening of valve and the metalsubstrate of the safety valve element for a battery are attached eachother in such a manner that the perforated pore of the metal substrateand the perforated pore of the closing plate are connected through, andthen both is adhered around the perforated pore of the closing plateusing adhering means.

Furthermore, the present invention is a closed battery characterizedthat an electrode comprising a positive electrode, a negative electrodeand a separator is packed with electrolyte into a battery container andan opening portion of the battery container is closed so that theclosing plate for battery is put into and fixed around innercircumference of the opening portion of the battery container.

A closed battery using a closing plate of the present invention containsa lithium fluoride as a supporting electrolyte, and metallic materialscomprising a battery container and safety valve element are notcorroded. But the fluoride absorbs moisture in the atmosphere and changeinto hydrofluoride acid which has strong corrosion. When non aqueouselectrolyte having such a strong corrosion scatters and sticks to theoutside of a battery container, a metal foil of a safety valve element,in particular, the thin metal foil is corroded and perforated. In caseof the safety valve element of the present invention, since it has aprotection film on the metal foil, the thin metal foil is neithercorroded nor perforated.

1. A method of forming a protection film of a safety valve element for abattery comprising providing a metal substrate having a hole extendingtherethrough, laminating a metal foil directly to said metal substrateso as to cover said hole, and applying an organic coating on at leastone side of said metal foil.
 2. The method of claim 1, wherein saidorganic coating is an organic resin film.
 3. A method of forming aprotection film of a safety valve element for a battery comprisingproviding a metal substrate having a hole extending therethrough,laminating a metal foil directly to said metal substrate so as to coversaid hole, and applying an organic coating on at least one side ofcovering portions of said metal foil.
 4. A safety valve element for abattery comprising a metal substrate having a first hole extendingtherethrough and a metal foil laminated directly to said metal substrateso as to cover said first hole, wherein a protection film is covered onat least one side of said safety valve element for a battery.
 5. Asafety valve element for a battery comprising a metal substrate having afirst hole extending therethrough and a metal foil laminated directly tosaid metal substrate so as to cover said first hole, wherein aprotection film is covered on at least one side of covering portions ofsaid metal foil of a safety valve element for a battery.
 6. A safetyvalve element for a battery according to claim 4, wherein saidprotection film is a continuous coated film of an organic coating.
 7. Asafety valve element for a battery according to claim 4, wherein saidprotecting film is an uncut laminated film of an organic resin film. 8.A safety valve element for a battery according to claim 5, wherein saidprotection film is a coated film of organic coating.
 9. A safety valveelement of a battery according to claim 8, wherein said protecting filmis a laminated film of an organic resin film.